Aim: Leaf and air temperatures are seldom equal, but many vegetation models assume that they are. Land-surface models calculate canopy temperatures, but how well they do so is unknown. We encourage consideration of the leaf-and canopy-to-air temperature difference (Delta T) as a benchmark for land-surface modelling and an important feature of plant and ecosystem function. Location: Tropical SW China. Time period: 2013. Major Taxa studies: Tropical trees. Methods: We illustrate diurnal cycles of leaf-and canopy-to-air temperature difference (Delta T) with field measurements in a tropical dry woodland and with continuous monitoring data in a tropical seasonal forest. The Priestley-Taylor (PT) and Penman-Monteith (PM) approaches to evapotranspiration are used to provide insights into the interpretation and prediction of Delta T. Field measurements are also compared with land-surface model results obtained with the Joint U.K. Land Environment Simulator (JULES) set up for the conditions of the site. Results: The Delta T followed a consistent diurnal cycle, with negative values at night (attributable to negative net radiation) becoming positive in the morning, reaching a plateau and becoming negative again when air temperature exceeded a 'crossover' in the 24-29 degrees C range. Daily time courses of Delta T could be approximated by either the PT or the PM model, but JULES tended to underestimate the magnitude of negative Delta T. Main conclusions: Leaves with adequate water supply are partly buffered against air-temperature variations, through a passive biophysical mechanism. This is likely to be important for optimal leaf function, and land-surface and vegetation models should aim to reproduce it.